1. Field of the Invention
The present invention relates to a call charge management device connected to one private branch exchange in a private branch exchange system for managing telephone call charges for extension telephone sets connected to a plurality of private branch exchanges, and more particularly to a call charge management device capable of performing appropriate call charge management in a private branch exchange system including a plurality of private branch exchanges connected thereto through private lines.
2. Description of the Related Art
Conventionally, a call charge management device connected to a private branch exchange for managing call charges for a plurality of extension telephone sets connected to the private branch exchange has been so arranged that, when a call is originated from any one of the extension telephone sets, the call charge management device calculates a call charge on the basis of a communication time and a distance between a calling telephone set and a called party determined from a place where the private branch exchange is installed, and charges the calling extension telephone set the calculated charge for that telephone call.
Recently, there has been proposed a private branch exchange system which comprises a private branch exchange as a system base and a station connected to the private branch exchange through a private line and installed in a charge area different from a charge area where the private branch exchange is installed. That is, the system extends over the different charge areas. In the private branch exchange system of this type, the private branch exchange as the system base accommodates a plurality of extension telephone sets and a plurality of office lines which are connected to a public network. The private branch exchange is connected through the private line to the station which is connected to the public network and which is installed in a charge area different from a charge area where the private branch exchange is installed. The private branch exchange is also connected to a call charge management unit for performing telephone call charge management for the plurality of extension telephone sets.
When a call is originated from an extension telephone set connected to the private branch exchange as the system base to another telephone set connected to the public network, there are two possible routes to choose from, one being a route connecting directly to the public network through the exchange and the other one being a route connecting to the public network through the station connected to the exchange through a private line.
Conventionally, the call charge management device in the private branch exchange system of this type has been configured to calculate the call charge on the basis of a communication time and a distance to a called party determined from a place where the private branch exchange is installed and to charge the calling extension telephone set the calculated call charge even when any one of the above two routes is selected.
According to such configuration, an accurate call charge cannot be charged for each of the extension telephone sets.
Assume, for example, that an extension telephone set connected to the private branch exchange as the system base places a call through a station, which is connected through a private line to the exchange and installed in a charge area different from the charge area where the exchange is installed, to communicate with a destination telephone set connected to a public network. In this case, the conventional call charge management device calculates the call charge on the basis of the communication time and the distance between the called telephone set and the exchange as the system base and charges the calling telephone set the calculated call charge.
However, the private line is used between the station and the exchange as the system base. Thus, if the distance calculated from the place where the exchange as the base system locates is used to calculate the call charge, the calculated call charge will be different from an actual amount and hence appropriate call charge management cannot be ensured.